Switched reluctance (SR) motors have gained popularity over the years due to their low-cost construction and high speed/torque performance.
The present disclosure relates to SR motors control devices and methods.
An SR motor is energized phase by phase in sequence, to generate reluctance torque and enable smooth motor rotation. The number of strokes (N) in an SR motor per one revolution of the rotor is dependent on the number of phases (M) of the stator and the number of rotor poles (P). It is given by the following relation:N=M×P  (1)
Therefore, the stroke angle (S) in mechanical degrees is defined as:S=360°/N  (2)
When the number of poles is very large and the stroke angle is very small, the SR motor is typically operated in open loop as a variable reluctance stepper motor and needs no knowledge of rotor position information during running condition. On the other hand, when the number of poles is small and the stroke angle is very large, the SR motor is generally operated in closed loop during running condition and hence, the knowledge of accurate rotor position information is very important to rotate the motor.
Accurate rotor position information may be obtained from a shaft position sensor. However, shaft position sensors are expensive and have reliability problems and hence, sensorless operation of SR motors has become a challenging alternative for designers.
There thus exist techniques for driving SR motors without a shaft position sensor. For instance, in a shaft position sensorless SR motor, a rotor angular position can be estimated according to various methods, which are typically based on the flux-linkage and the inductance characteristics of the motor with respect to the rotor position.
For instance, U.S. Pat. No. 6,448,736 discloses a method of controlling an SR motor comprising a step of aligning the motor, which is carried out once, followed by steps of energizing and de-energizing the stator phases and of monitoring the phase current in the stator phases of the SR motor, which are then continuously repeated. The step of aligning the motor comprises energizing one single phase of the motor. Because only one phase of SR motor is supplied during alignment, the rotor aligns under this phase. However, unwanted rotor oscillations during the alignment cause significant time for the rotor to settle. These oscillations stem, in particular, from the asymmetry of the rotor which provides that the motor always starts rotating in the right direction. In practise, the rotor stabilization may take up to a few seconds, for instance no less than 2 seconds.